Breast cancer is the most common cancer in women across the US as well as developed and developing regions across the world. There are over 10 million Americans who live with a personal history of cancer and are thus considered to be cancer survivors. Among survivors, fear of cancer recurrence (FOR) is the most prevalent psychosocial concern and can be more pronounced for partners and caregivers than for the patients themselves. Despite substantial anecdotal, clinical, and cross-sectional evidence, at present there is surprisingly little known empirically about the temporal course of FOR or the factors that predict prospectively who will suffer from chronic and/or severe FOR. The behavioral research proposed in this R21 application will be the first comprehensive and intensive investigation into the everyday as well as longer-term predictors of FOR in the lives of BC survivors and their spouses/partners. This work has important implications for clinical practice guidelines for the psychosocial care of BC survivors (both patient and their significant others) including effective psychosocial-focused assessment, intervention services, and cancer survivorship programming. The proposed work represents the next step in an ongoing collaboration between behavioral science researchers at the University of Delaware and Helen F. Graham Cancer Center (an NCI-designated Community Cancer Center part of Christiana Care Health System, Newark, DE).